<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
<style>
    *{
        margin:0;
        padding:0;
    }
    .b1{
        width:500px;
        height:1000px;
        background-color: yellowgreen;
        margin:0 auto;
    }
    body{
        background-image: url(zhihu.png);
        background-size: cover;
        background-attachment: fixed;
    }
</style>
</head>
<body>
    <div class="b1"></div>
</body>
</html>